Question

An object is placed at a distance of 30cm from a concave lens of focal length 15cm. List four characteristics of the image formed by the lens. No need of diagram. 2marks ​

Answer 1

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u=-30cm f= -15cm

1/f=1/v-1/u

1/v=1/f+1/u

on substituting v=-10cm

m=v/u

m=-10/-30

m=1/3=.33

so the magnification is positive so it is a virtual erect image .

m is less than 1 so the image is diminished .

and v is negative so the image is formed on the same side of the lens.

Answer 2

Given

u=-30cm and f=-15 cm

1/v-1/u=1/f

1/v-1/(-30)=1/(-15)

1/v=-1/15-1/30

1/v=-2-1/30

-3/30

-1/10

v=-10.

Image formed is virtual

image formed is erect

diminished

concave lens on the left side